A further contribution to the internal energy of a material structure originates from the thermally-induced lattice vibrations (phonons). These are particularly significant at high temperatures, but in the context of DFT computations performed at zero temperature they are typically negligible in terms of their energetic contribution. This contribution however remains finite and positive in magnitude due to quantum residual effects. This "Zero-point Energy"1 contribution to the internal energy of a zero-temperature solid can thus be computed separately.